Abstract
UDP-D-galacturonate, the precursor for the galacturonic acid residues in pectic polysaccharides, is synthesized through the activity of UDP-D-glucuronate 4-epimerase. The enzyme from pea or radish has been reported to be associated with membranes. A BLAST search with the protein sequence of Streptococcus pneumoniae UDP-D-glucuronate 4-epimerase identified six putative isoenzymes in Arabidopsis. The predicted cytoplasmic domain of one isoform (At4g30440) was expressed in Escherichia coli. The recombinant protein catalyzed the conversion of UDP-D-glucuronate into UDP-D-galacturonate, confirming that the gene encodes UDP-D-galacturonate in Arabidopsis. The subcellular localization of the enzyme is now under investigation using the antibody raised against the recombinant protein.
